This invention relates to a system and method for diagnosing an evaporative emission control system of an internal combustion engine.
Vehicle internal combustion engines employ numerous subsystems to effect their operation. The subsystems include, for example, spark timing control, fuel control, and evaporative emission control. The failure of any of the engine subsystems may detrimentally affect the operation of the internal combustion engine in terms of either performance or emissions. Therefore, it is desirable to be able to diagnose the various subsystems of an internal combustion engine so as to evaluate whether or not the subsystem is operating in a satisfactory manner. This invention is directed toward a system and method for diagnosing the operation of the evaporative emission control system of an internal combustion engine.
Engine evaporative emission control systems typically use a fuel vapor recovery canister to control the loss of fuel vapors from vehicle fuel tanks. Generally the canisters take the form of a container filled with activated charcoal or some other absorbing agent which is effective to store the evaporated hydrocarbons until they can be drawn into the induction system of the engine to undergo combustion in the engine cylinders. In these systems, the vacuum in the intake manifold of the engine is used to draw a purge stream of air through the canister so as to purge the collected vapors from the active material of the canister during each engine operation so as to condition the canister for collection of subsequently generated vapors.
These evaporative emission control systems are generally comprised of a combination of hoses, pipes and containments, such as the vapor collection canister and the fuel tank, connected with defined openings to the environment. Defects in such a system will typically show as a leak resulting from, for example, disconnected hoses or a loose or missing gas cap. Defects may further take the form of a restriction such as a pinched line.